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SOHO Joint Observing Programme 067
INVESTIGATION OF THE STRUCTURE OF THE LOWER CORONA AND THE CONTRIBUTION
OF SMALL EJECTA TO THE SOLAR WIND.
Authors: Mark Lyons (LASCO, Birmingham), Richard Harrison (CDS, RAL),
Ester Antonucci (UVCS, Torino), Don Michels (LASCO, NRL),
Philippe Lemaire (SUMER, Orsay),
Ludwig Klein (Paris-Meudon Observatory, France),
Henry Aurass & Gottfried Mann (Astrophysical Institute Potsdam, Germany)
E-mail Addresses:
mal@star.sr.bham.ac.uk
harrison@solg2.bnsc.rl.ac.uk
antonucci@to.astro.it
michels@maple.nrl.navy.mil (local coordinator at GSFC)
lemaire@sumop1.nascom.nasa.gov
ludwig.klein@obspm.fr
haurass@aip.de
gmann@aip.de
Progress:
Fourth Draft July 22, 1997
Objective:
To observe the stucture and evolution of the lower corona (1-2.8R) and
the onset phase of the small CME 'blobs' in the
streamer belt with EUV, UV and white-light data.
Conditions Necessary to Run:
We require, at a minimum, the synoptic operation of LASCO,
with sufficient numbers of C1 images and C2/3 images to
identify 'blob' events. Ideally, we would like CDS, UVCS and
SUMER observing the limb region. At a minimum, any one of
these should be in operation.
Scientific Case:
LASCO has identified in C2 and C3 small ejecta in the streamer belts,
often referred to as blobs, which are first detected around 3 R.
These events have been interpreted as tracers of the slow solar wind
(Sheeley et al. ApJ, 1997 (in press)). C1 has viewed the ejection
of small balloon-like CMEs between closed loop structures. These
loops do not seem to be significantly disrupted by these CMEs and the
foot-point positions of the overlying streamer belts also do not vary
much with time. In addition, X-ray observations with Yohkoh have
shown the frequent expansion of hot loops into the high corona. It is
essential to identify these activities in various wavelengths in
order to investigate the physical connection between them and to
understand the structure of the lower corona.
We wish to determine the onset processes of the small blob-like
events and to determine their relationship with the Yohkoh-type
loops and the other events seen by LASCO. As well as investigating
their onsets, any observations which can provide information on the
mass ejected and the event rates can provide an estimate for the
contribution these events make to the slow solar wind.
The non-ideal evolution of coronal structures should be
revealed by energy release processes such as heating and
particle acceleration. Coherent radio emission at decimetric
and metric wavelengths is a sensitive tracer of non-Maxwellian
electron populations (beams or loss-cone distributions) in
the corona, both during flares and in events where much smaller
amounts of energy are released in association e.g. with bright
points or quiescent active regions. The radio observations
will look for such signatures of coronal reconfiguration,
with the attempt to identify the spectrum and the site of the
nonthermal emissions.
Basic Method:
LASCO should operate the synoptic programme - but ensure
good C1 and C2 coverage of the west limb. UVCS should be directed to
the region above the west limb (at 1.7R). CDS and SUMER
should target the limb itself or be just off the limb. The
radio instruments will operate as detailed below.
Pointing and Target Selection:
Pointing must be to the west limb to ensure collaboration with
SUMER and to allow observation of the structures being viewed
prior to their arrival at the limb.
Operating Details:
CDS - 12x4 arcminute field of view formed from three 4x4 arcminute
rasters, in approximately 6 lines, as follows;
Ion Wavelength Temperature
He I 584 A 20,000 K
O V 629 A 250,000 K
Mg IX 368 A 1,000,000 K
Fe XVI 360 A 2,000,000 K
Si X 347 A 1,000,000 K ) Density sensitive
Si X 356 A 1,000,000 K ) line pair.
Long axis of the field should be directed N-S.
The field should be centred either
on the limb or just off-limb, probably just north or
south of the equator. The latest C1 images should be
used and CDS should sit such that the 12x4 field extends
just north or south enough to see the edge of the
streamer.
Cadence time 15 minutes or longer, possibly with
two exposures set for observations on disc or limb.
SUMER - Observations will be taken about 30" above the western limb.
The 4 x 300 arcsec^2 slit will be used every minute during
8 hours to provide profiles of
O IV, 790 A
N IV, 765 A
O V, 760 A
Ne VIII, 765 A.
These can be repeated as necessary.
UVCS - Sit & Stare at 1.7 Ro.
Nominal UV (LYA and OVI channels)+ VL observation of 8h
(+30m for trasmission and mechanisms delays).
Pointing Total Dwell Exp time x repetitions
----------------------------------------------
1.7 Ro 28800 200 sec x 144
Mask details:
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LYA OVI
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Slit width 50 um 35 um
Grating Pos 110000 225000
Mask LYA_CME110 OVI_CME225
Spatial Bin 5pix(35") 6pix(42")
Number of panels 5 5
Selected spatial range 36-355 (64 bins) 15-338 (54 bins)
Spatial bins trasmitted 64 64
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Spectral Range column interval column interval
Panel # 0 295-334 (20x2) 101-236 (136x1)
Si II 1264.74 Si XII 520.66
OVI 1037.61
OVI 1031.91
Panel # 1 446-511 (66x1) 248-313 (33x2)
Fe XII 1242 H Ly-b 1025.72
N V 1238.82
Panel # 2 598-701 (104x1) 536-557 (22x1)
Ly-a 1215.67 Si XII 499.37
Panel # 3 702-749 (48x1) 608-647 (40x1)
Si III 1206.51 N III 991.58
N III 989.79
Panel # 4 750-823 (74x1) 748-828 (81x1)
S X 1196.24 C III 977.02
H Ly-g 972.54
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Tot. spectral bins 312 312
Bins per channel 64x312=19968 64x312=19968
Mask Trasmission time 101 s 101 s
LASCO - The present synoptic programme will be run placing emphasis on higher
cadence C2 one-limb observations, whenever possible. The western
limb will be favoured for the reasons outlined above in
the pointing selection. Longer exposure C1 images in Fe XIV
and Fe X will be taken to help investigate the region of
overlap between the C1 and C2 fields of view.
RADIO - Two complementary instruments will be used for this study.
The whole-Sun flux density spectrum will be obtained by the Tremsdorf
spectrograph of the Potsdam Astrophysical Institute in the
range 40 to 800 MHz, i.e. roughly between the base of the
corona and two solar radii above the photosphere
(observing time: 7-15 UT). Images of the Sun will be
provided by the Nancay Radioheliograph at five frequencies in
the range 150 to 450 MHz (observing time: 8-16 UT)